Published online by Cambridge University Press: 15 May 2009
1. Rabbit cells show a marked variation in agglutination when reacting with apparently homologous iso-antisera.
2. This phenomenon has been investigated in two ways:
(a) Samples of apparently homologous antisera have been absorbed with (i) strongly agglutinating cells, (ii) poorly agglutinating cells. It was found that strongly agglutinating cells absorbed the antibody completely and rapidly from the serum, whilst poorly agglutinating cells, though they absorbed it completely, did so much more slowly. Also, when a serum which had been absorbed with poorly agglutinating cells until these no longer reacted with it was titrated against strongly agglutinating cells, these were still strongly agglutinated. This showed a source of serious error when investigating new sera by absorption techniques and when using weak antisera for grouping purposes.
(b) Poorly agglutinating cells were injected into rabbits, and the antisera so obtained were examined against strongly agglutinating cells and against the poorly agglutinating cell used as the antigen. The antibody response was poor; two out of eight rabbits developed an antibody, and strongly agglutinating cells reacted more strongly with these antisera than the poorly agglutinating cells which had been used as the antigen.
3. Three hypotheses for this variation in agglutination have been put forward and discussed:
(a) That the variation is due to cross reactions between numbers of closely related antigen-antibody systems. The results of the investigations 2 (a) and 2(b) suggest that this is unlikely.
(b) That the disposition of antigen sites on the surface of the red cell is a factor determining the agglutinability of the cell. It is considered that this might play a subsidiary role in the phenomenon as it is shown in the rabbit.
(c) That rabbit red cell agglutinability is mainly determined by the number of antigen sites on the cell available to the antibody. The experimental results can be explained on this hypothesis, and it is suggested that this may be the main factor accounting for the behaviour of rabbit red cells. It is pointed out that supporting evidence for this is afforded by measurements with radio iodinated antisera.